On convective stability of the equilibrium of col-loids and liquid binary solutions with positive thermal diffusion

Abstract

The study investigates stability of the mechanical equilibrium of colloids and binary mixtures with positive thermal diffusion. Such problems are usually considered in the presence of a stationary concentration distribution that arises due to thermal diffusion and (or) sedimentation. But in connected vertical channels of a square section of 3.2×3.2 mm with a height of 50 mm, a Hele-Shaw cell of 17×32×1.5 mm, and a flat layer with a height of 3 mm when heated from below, the time it takes the concentration profile to become settled is extremely long and ranges from several days to several years. Therefore, the stability of the equilibrium was analyzed in the presence of increasing concentration inhomogeneities. This helped explain the experimental facts: 1) periodic (~4 hours) convective bursts were observed in the magnetic fluid in channels below the critical Rayleigh number; 2) bursts with a period of ~0.5 hours were observed in the binary mixture in the Hele-Shaw cell. A formula for the period of bursts has been obtained, it gives results close to experimental ones.